A noun is a part of speech that names a person, place, thing, idea, or activity. Some nouns are specific for people, places, or events; and some represent groups or collections. Some nouns aren't even technically labeled nouns as their part of speech; they're verbs acting like nouns in sentences.
Nouns can be singular, referring to one thing, or plural, referring to more than one thing. Nouns can be possessive, indicating ownership or a close relationship. Regardless of the type, nouns should always agree with their verbs in sentences. Use singular verbs with singular nouns and plural verbs with plural nouns. You have to know how a noun works in order to write an effective sentence.